A portable radio is typically understood to be a radio device capable of being carried on or about the person. FIG. 1 illustrates a conventional portable radio 10. The portable radio 10 includes a display 12 and a speaker 14 by which data and voice message are respectively presented to the radio operator. A keypad area 16 and a microphone (typically mounted behind the speaker grill and not visible in FIG. 1) enable the radio user to originate calls and participate in communications with other radio operators. To control the operation of the radio 10, control knobs 18 are used to change parameters, enable or disable functions, and otherwise modify the performance of the radio. Also, the radio 10 is controlled by a push-to-talk (PTT) switch 20, which is activated whenever the operator desires to transmit.
While portable radios are readily operable as hand-held devices, it is customary for portable radio users to carry ("wear") their radio about hip level either by virtue of a clip arrangement or by using a carry-case. However, some portable radio users dislike having to repeatedly pickup and return their portable radio to the carry case. Moreover, since the speaker 14 is ordinarily at hip level, it is sometimes difficult to hear messages communicated via the radio.
Accordingly, many portable radio users prefer to use a radio accessory commonly referred to as a remote speaker/microphone 22. The remote speaker/microphone 22 is coupled to the radio 10 via cable 24 that contains one or more wires so that data and voice messages received by the radio 10 may be presented to the operator by the display 12' and 14' respectively. Also, a keypad 16' and microphone (typically mounted behind the speaker grill and not visible in FIG. 1) enable the radio operator originate and participate in calls by activating the PTT switch 20' without having to physically moving the radio from the hip level position. Ordinarily, the remote speaker/microphone 22 is worn (carried) either at the operator's shoulder level or shirt-pocket level. Accordingly, since the speaker 14', display 12', and microphone are conveniently positioned near the operator's head, messages can be heard, displays can be read, and transmissions may be made more conveniently.
Regrettably, the use of a speaker/microphone 22 results in a rather significant detriment. As is known, the radio 10 transmits information by radiating electromagnetic energy from its antenna 26. This radiated energy is picked up by the cable 24, which acts like a receiving antenna and couples unwanted electromagnetic energy into the remote speaker/microphone 22 and the radio 10. The coupled electromagnetic radiation tends to re-bias electronic circuits and devices within the radio 10 and the remote speaker/microphone 22 degrading their performance to an unacceptable level.
Some radio designers have attempted to compensate for this detriment by incorporating intricate electromagnetic shielding arrangements into their portable radios. However, designing such shielding arrangements is complicated and time consuming. Moreover, the additional of electromagnetic shields increase radio cost, and often, provides only a margin improvement in radio performance. Accordingly, a need exists to provide a remote control accessory for a radio that avoids the problems of the prior art.